Polypropylene resins are produced in tremendous amounts for various purposes. Polypropylenes are particularly useful as molding resins having low density, high hardness, chemical inertness. Polypropylene by itself has inadequate impact strength for many purposes, unless blended with other materials, or unless specially made polypropylene block copolymers are prepared.
However, the low temperature impact strength of polypropylene can be improved by blending with polymers of various types. Some of the blends have been successful in improving impact strength at low temperature, but have had undesirable side effects. For example, blending polypropylene with polyisobutylene as a modifier improves impact strength, but decreases flexural modulus.
An improved approach blends polypropylene with a rubbery block copolymer of a conjugated diene/monovinylarene character, such as a butadiene/styrene block copolymer. This improves low temperature impact strength of the polypropylene, but at the same time minimizing decreases in flexural modulus.
Remaining has been a problem of loss in tensile of the polypropylene/rubber blend after high temperature aging. Efforts have been made to alleviate this problem in the polypropylene/conjugated diene monovinylarene blends by employing a further component such as an EPDM terpolymer such as described in U.S. Pat. No. 4,258,145 to Wright.
However, the basic need for improvement or avoidance in loss in tensile of the basic blend after high temperature aging still requires a solution.